1. Field of the Invention
Example embodiments of the present invention relate to slurry compositions and methods of polishing a layer using the slurry compositions. More particularly, example embodiments of the present invention relate to slurry compositions used for performing a high-planarity polishing process, and methods of polishing a layer using the slurry compositions.
2. Description of the Related Art
In manufacturing a semiconductor memory device, structures having a level upper face are required to be formed on a semiconductor substrate. The structures are generally formed by performing several processes such as a deposition process, a patterning process, an etching process, a polishing process, etc. Particularly, a chemical mechanical polishing (CMP) process is frequently used for forming the structures.
In the CMP process, a semiconductor substrate to be polished is located on a wafer carrier, and then a slurry composition including an abrasive is provided to a polishing pad. While the semiconductor substrate is in contact with the polishing pad, the semiconductor substrate and the polishing pad are rotated together and pressurized. As a result of polishing the semiconductor substrate, a surface of the semiconductor substrate is planarized. Particularly, the surface of the semiconductor substrate is mechanically polished by rubbing the surface of the semiconductor substrate with the abrasive included in the slurry composition and a rugged surface of the polishing pad. Simultaneously, the surface of the semiconductor substrate is chemically polished by reacting chemical components of the slurry composition with surface substances of the semiconductor substrate.
The polishing efficiency of the CMP process may be determined by the CMP apparatus, the chemical composition of the slurry composition, the type of the polishing pad, etc. The chemical composition of the slurry composition may have an important effect on the polishing efficiency.
A single slurry composition may exhibit different polishing rates between various layers in accordance with properties or types of layers to be polished. Thus, layers are selectively polished, for example, one of an oxide layer, a nitride layer, a polysilicon layer and a metal layer, which are widely used in manufacturing a semiconductor device, may be selectively polished during the CMP process by using the differences in the polishing rates.
A high planarity slurry chemical mechanical polishing (HPS-CMP) process has been developed so as to improve a planarity of a layer having a highly stepped upper portion. A slurry composition including a passivating agent such as an ionic surfactant may be used for performing the HPS-CMP process.
In the HPS-CMP process, the ionic surfactant in the slurry composition may be electrically adsorbed onto a surface of a silicon oxide layer to form a polish stop layer on the silicon oxide layer. Therefore, a chemical polishing process may be suppressed from being performed, so that a mechanical polishing process may be mainly performed in the HPS-CMP process. A stepped upper portion of the silicon oxide layer is mechanically polished from a top surface thereof. As the silicon oxide layer is planarized, a contact area between the silicon oxide layer and the polishing pad may increase, and a polishing pressure applied to the silicon oxide layer may be dispersed. Due to the dispersion of the polishing pressure, a polishing rate of the silicon oxide layer may be greatly reduced and the planarized silicon oxide layer may function as a polish stop layer. Therefore, the silicon oxide layer having a high planarity may be formed through the HPS-CMP process. However, when the HPS-CMP process is performed on a layer including a high height portion formed on dense structures and a low height portion formed on sparse structures adjacent to the dense structures, the HPS-CMP process may not exhibit the polish stop characteristics, and thus the structures formed on a substrate may be damaged. Furthermore, the HPS-CMP process may require a polishing time, which is about four to about five times longer than that of a conventional CMP process, and thus the HPS-CMP process has not been considered economically acceptable.
Therefore, there have been ongoing researches to develop slurry compositions that may be used for polishing a layer with a high planarity through the HPS-CMP process and reduce a polishing thereof, however methods of developing such slurry compositions have not been found yet.